PrEP side effects: what to expect in your first month

Starting PrEP (Pre-Exposure Prophylaxis) is one of the most effective steps you can take to protect yourself from HIV. If your healthcare provider has prescribed PrEP and you are about to begin your first month, you are probably wondering what to expect physically. Will you feel different? Will the side effects be difficult to handle? These are completely valid questions, and the short answer is reassuring: most people tolerate PrEP very well, and the side effects that do occur are typically mild and temporary.

This article will walk you through the common side effects, how long they usually last, practical tips for managing them, and the warning signs that should prompt you to contact your doctor. If you have not yet started PrEP and need to find a provider, browse our facility directory or connect with a community-based screener near you. As a medical technologist, I will also explain the lab tests involved in PrEP monitoring so you understand exactly what your healthcare team is looking for at every checkup.

Starting PrEP is a positive step

Before we talk about side effects, it is worth pausing to recognize what starting PrEP means. You are taking a proactive, evidence-based step to protect your health. PrEP is up to 99% effective at preventing HIV when taken daily as prescribed. The fact that you are informed enough to seek out this medication and disciplined enough to commit to taking it every day puts you in a strong position.

Every medication has potential side effects, from common over-the-counter painkillers to prescription drugs. The side effects associated with PrEP are generally mild, well-studied, and short-lived. Understanding what to expect helps you stay on track during the adjustment period instead of stopping prematurely.

Common side effects in the first month

The most commonly reported side effects of PrEP (tenofovir disoproxil fumarate/emtricitabine, or TDF/FTC) occur during the first few weeks as your body adjusts to the medication. Clinical trials and real-world studies consistently show that these effects are mild and self-limiting for the vast majority of users.

Nausea

Nausea is the most frequently reported side effect, affecting roughly 10% of people who start PrEP. It is usually described as a mild, queasy feeling rather than severe vomiting. Many users compare it to the sensation you get when you take a vitamin on an empty stomach. Nausea tends to be most noticeable during the first one to two weeks and gradually fades as your body adjusts. Taking PrEP with food significantly reduces the likelihood and severity of nausea.

Headache

Headaches affect approximately 7% of new PrEP users. These are typically mild tension-type headaches rather than migraines. Staying well-hydrated and maintaining a regular sleep schedule can help minimize headaches. Over-the-counter pain relief like paracetamol (acetaminophen) is safe to use alongside PrEP if needed. If headaches persist beyond the first month, talk to your healthcare provider.

Fatigue and dizziness

Some users report feeling slightly more tired than usual or experiencing occasional lightheadedness during the first few weeks. This affects around 6% of new users. The fatigue is generally mild and does not interfere with daily activities. It often resolves on its own within two weeks. Getting adequate sleep and maintaining consistent meal times can help your body adjust more smoothly.

Stomach discomfort, gas, and bloating

About 5% of people notice gastrointestinal symptoms such as mild stomach cramps, increased gas, or a feeling of bloating. These symptoms are related to the way your digestive system processes the medication. Eating smaller, more frequent meals instead of large ones can ease discomfort. Avoiding very fatty or spicy foods during the first week may also help.

Decreased appetite

A small number of users, roughly 4%, report a temporary reduction in appetite. This is closely related to the mild nausea some people experience. Appetite typically returns to normal within two to three weeks. Even if your appetite is reduced, try to eat regular meals so that your body has the fuel it needs and the medication is absorbed properly.

How long do side effects last?

The medical community often refers to the initial adjustment period as the "start-up syndrome." This term reflects the fact that side effects are concentrated in the early weeks and then resolve. Here is what a typical first month looks like:

Clinical studies of TDF/FTC for PrEP, including the landmark iPrEx trial, found that start-up side effects resolve in the vast majority of participants within two to four weeks. Fewer than 2% of participants in major clinical trials discontinued PrEP because of side effects.

Tips for managing side effects

You do not have to simply wait out the adjustment period without doing anything. Several practical strategies can make the first few weeks more comfortable:

• Take PrEP with food. This is the single most effective way to reduce nausea and stomach discomfort. Even a small snack like crackers or a banana is enough.
• Take it at bedtime. Many users find that taking their daily dose before bed allows them to sleep through the peak period when nausea might occur. By morning, the sensation has usually passed.
• Stay hydrated. Drinking plenty of water throughout the day helps your kidneys process the medication efficiently and can reduce headaches and fatigue.
• Give your body time. Knowing that the adjustment period is temporary makes it easier to push through. Mark the two-week and four-week milestones on your calendar so you can track your progress.
• Avoid alcohol during the first week. While moderate alcohol consumption is generally considered safe with PrEP, avoiding it during the first few days can reduce stomach irritation while your body is adjusting.
• Keep a brief symptom diary. Jotting down what you feel each day helps you notice improvement and gives your healthcare provider useful information at your follow-up appointment.

Rare but serious side effects

While the common side effects discussed above are mild and temporary, PrEP does carry a small risk of more significant effects that require medical monitoring. This is why regular follow-up appointments and lab tests are a non-negotiable part of being on PrEP.

Kidney function changes

Tenofovir disoproxil fumarate (TDF), one of the two active ingredients in PrEP, is processed by the kidneys. In a small percentage of users, TDF can cause a mild and usually reversible decline in kidney function. This is measured through blood tests that check your creatinine level and estimated glomerular filtration rate (eGFR). In clinical trials, clinically significant kidney effects occurred in fewer than 1% of PrEP users, and kidney function returned to normal after discontinuing the medication.

This is precisely why your healthcare provider will check your kidney function before you start PrEP and at regular intervals afterward. If any changes are detected early, your provider can adjust your treatment plan before any lasting damage occurs.

Bone mineral density

Some studies have found that TDF-based PrEP can lead to a small decrease in bone mineral density, typically around 1-2%. This reduction is considered clinically insignificant for most people and is reversible after stopping PrEP. It is generally not a concern for otherwise healthy adults. However, if you have a pre-existing condition that affects your bones, such as osteoporosis, your provider should be made aware so they can monitor accordingly.

Lactic acidosis

Lactic acidosis is an extremely rare but potentially serious condition in which lactic acid builds up in the bloodstream. It has been associated with nucleoside reverse transcriptase inhibitors (NRTIs) as a drug class, but documented cases specifically linked to PrEP dosing are vanishingly rare. Symptoms include unusual muscle pain, difficulty breathing, stomach pain with nausea and vomiting, and feeling cold or dizzy. If you experience these symptoms together, seek medical attention immediately.

Your monitoring schedule on PrEP

Regular monitoring is a cornerstone of safe PrEP use. Your healthcare provider will schedule checkups at specific intervals to ensure the medication is working well and not causing any unwanted effects.

What lab tests are involved

As a medical technologist, I want to demystify the laboratory side of PrEP monitoring. Understanding what each test measures can help reduce anxiety about your checkups.

HIV antigen/antibody test (4th generation). This combination test detects both HIV antibodies (produced by your immune system in response to the virus) and the p24 antigen (a protein found on the surface of HIV). It is the standard screening test used at every PrEP visit. You must be confirmed HIV-negative before each prescription refill because taking PrEP while HIV-positive can lead to drug resistance. Learn more about how to get tested for HIV in the Philippines.

Serum creatinine and eGFR. Creatinine is a waste product produced by your muscles and filtered by your kidneys. When kidney function declines, creatinine levels rise. The eGFR (estimated glomerular filtration rate) is calculated from your creatinine level along with your age, sex, and body size. It gives a more accurate picture of how well your kidneys are filtering. A normal eGFR is above 90 mL/min. PrEP is generally not recommended if your eGFR falls below 60 mL/min.

Hepatitis B surface antigen (HBsAg). This test checks whether you are infected with hepatitis B. TDF/FTC is also active against hepatitis B, so if you have chronic hepatitis B and stop PrEP abruptly, you could experience a flare-up of hepatitis. Your provider needs to know your hepatitis B status before prescribing PrEP.

STI screening. Depending on your risk profile and sexual practices, your provider may order tests for chlamydia, gonorrhea, and syphilis at each quarterly visit. These can be performed on urine samples, blood draws, or swabs depending on the sites of potential exposure.

Urinalysis. A routine urine test may be included to check for protein in the urine (proteinuria), which can be an early sign of kidney stress. This is a simple, non-invasive test that adds an extra layer of kidney monitoring.

When to contact your healthcare provider

While most side effects resolve on their own, you should reach out to your healthcare provider if:

• Nausea, headaches, or fatigue persist beyond four weeks without improvement
• You notice dark or brown-colored urine, which could suggest kidney issues
• You develop a skin rash that was not present before starting PrEP
• You experience unexplained muscle pain or weakness
• You have persistent abdominal pain that does not respond to dietary changes
• You notice unusual swelling in your hands, feet, or ankles
• You feel that the side effects are affecting your quality of life to the point where you are considering stopping PrEP

Never stop taking PrEP without consulting your provider first. If you are struggling with side effects, your provider may adjust your dosing strategy, check for underlying causes, or discuss alternative PrEP formulations that may suit you better. If you have had an actual exposure to HIV, ask about PEP (post-exposure prophylaxis) as a separate emergency option.

PrEP and interactions with other medications

PrEP (TDF/FTC) has relatively few drug interactions, but there are some important ones to be aware of:

• Non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and naproxen should be used sparingly while on PrEP, as both NSAIDs and TDF are processed by the kidneys. Occasional use is generally fine, but chronic daily use could increase the risk of kidney problems.
• Adefovir dipivoxil (used for hepatitis B treatment) should not be taken concurrently with PrEP, as both contain tenofovir-related compounds.
• Aminoglycosides and other nephrotoxic drugs should be used cautiously. Inform your provider about all medications you take.
• Hormonal contraceptives do not interact with PrEP. You can safely take birth control pills, injections, or implants alongside PrEP.
• Feminizing or masculinizing hormones do not have clinically significant interactions with TDF/FTC. Transgender individuals can take hormone therapy and PrEP concurrently.

Always bring a complete list of your medications, supplements, and herbal remedies to your PrEP appointments so your provider can check for potential interactions.

Frequently asked questions

Will PrEP make me gain weight? Large clinical studies have not found a significant association between PrEP and weight gain. Some people report minor fluctuations during the adjustment period, but these are typically related to appetite changes rather than the medication itself.

Can I drink alcohol while on PrEP? Moderate alcohol consumption does not reduce the effectiveness of PrEP or cause dangerous interactions. However, heavy drinking can affect your liver and kidneys, which are the organs that process PrEP. It is best to drink in moderation and stay well-hydrated.

What if I miss a dose during the first month? Take the missed dose as soon as you remember. If it is almost time for your next dose, skip the missed one and continue with your regular schedule. Do not take two pills at once. Missing an occasional dose is not ideal, but PrEP remains effective as long as you maintain high overall adherence. Set a daily alarm or use a pill organizer to stay consistent.

Do side effects mean the medication is working? Not necessarily. Side effects are your body's reaction to a new substance, not an indicator of whether PrEP is building protection. The medication works at the cellular level whether or not you feel any side effects.

Is there a PrEP formulation with fewer side effects? Tenofovir alafenamide/emtricitabine (TAF/FTC), sold as Descovy, has shown a more favorable kidney and bone safety profile compared to TDF/FTC in clinical trials. However, TAF/FTC availability and cost vary by location, and it has only been studied for HIV prevention via sexual contact in cisgender men and transgender women. Discuss with your healthcare provider whether TAF/FTC is available and appropriate for you.

Will PrEP affect my fertility? There is no evidence that PrEP affects fertility in either men or women. PrEP has also been studied in pregnant and breastfeeding women, with no significant safety concerns identified for the mother or child.

Sources and references

1. CDC. "About HIV." https://www.cdc.gov/hiv/about/index.html
2. HIV.gov. "What Are HIV and AIDS?" https://www.hiv.gov/hiv-basics/overview/about-hiv-and-aids/what-are-hiv-and-aids
3. WHO. "HIV/AIDS Fact Sheet." https://www.who.int/news-room/fact-sheets/detail/hiv-aids
4. Grant RM, Lama JR, Anderson PL, et al. Preexposure chemoprophylaxis for HIV prevention in men who have sex with men. N Engl J Med. 2010;363(27):2587-2599.
5. World Health Organization. Consolidated guidelines on HIV prevention, testing, treatment, service delivery and monitoring. Geneva: WHO; 2021.
6. Centers for Disease Control and Prevention. Preexposure prophylaxis for the prevention of HIV infection in the United States - 2021 update. Atlanta: CDC; 2021.
7. Baeten JM, Donnell D, Ndase P, et al. Antiretroviral prophylaxis for HIV prevention in heterosexual men and women. N Engl J Med. 2012;367(5):399-410.
8. Mugwanya KK, Wyatt C, Celum C, et al. Changes in glomerular kidney function among HIV-1-uninfected men and women receiving emtricitabine-tenofovir disoproxil fumarate preexposure prophylaxis. JAMA Intern Med. 2015;175(2):246-254.
9. Department of Health, Republic of the Philippines. National HIV/AIDS and STI Prevention and Control Program. Policy guidelines on the use of antiretroviral drugs for HIV prevention; 2022. https://doh.gov.ph/
10. Mayer KH, Molina JM, Thompson MA, et al. Emtricitabine and tenofovir alafenamide vs emtricitabine and tenofovir disoproxil fumarate for HIV pre-exposure prophylaxis (DISCOVER): primary results from a randomised, double-blind, multicentre, active-controlled, phase 3, non-inferiority trial. Lancet. 2020;396(10246):239-254.