Key points
- A drug interaction can affect the drugs’ effectiveness and side effects.
- It’s important to tell your doctor or pharmacist about all the medicines you are taking, including products you buy over the counter, herbal or traditional medicines, and recreational drugs.
- Older age and taking more drugs increase the risk for problems such as side effects or drug-drug interactions.
- The University of Liverpool provides an online tool to check for interactions.
Many people with HIV need to take medicines to treat other health conditions. Taking two or more different drugs together may change the effectiveness or side effects of one or more of the drugs. This is nearly always because drugs share the same metabolic pathway.
It is important that anyone prescribing or dispensing medication knows about all medicines and drugs that you are taking – this includes those prescribed by another doctor, over-the-counter medicines (including inhalers and nasal sprays), herbal and alternative treatments, hormones and contraceptives, and recreational drugs.
Some drug combinations are contraindicated – which means you definitely should not take them together. Reasons for this include serious side effects, or interactions which make one or both drugs ineffective or toxic.
Other interactions are less dangerous, but still need to be taken seriously. Levels of one or both drugs in your blood may be affected and you may need to change the doses you take.
Interactions are possible between HIV medicines and a wide range of other medication. This includes antihistamines, treatments for indigestion, hormonal contraceptives (birth control) and statins (drugs that are used to control cholesterol, or lipid levels). This includes medicines bought over the counter at high-street chemists (community pharmacies).
Checking for interactions
Your HIV doctor and pharmacist will check for possible interactions before they prescribe a new medication for you. You can help them do this by keeping a list of all the medicines and drugs you take (note down the name of each drug and what you take it for). Bring it with you whenever you see a doctor or pharmacist. If any other healthcare professional prescribes or recommends a medicine for you, it’s important that they know about the drugs you are taking for your HIV.
The University of Liverpool provides an online tool to check for interactions between anti-HIV drugs, other medications and recreational drugs. You enter the names of the medication you are taking and the results are provided with a traffic-light system: if the result is red or amber, it’s worth checking with your doctor or pharmacist. If it’s green, there shouldn’t be any problem. Visit www.hiv-druginteractions.org/checker or download the Liverpool HIV iChart app for iPhone or Android.
You can find out more about possible interactions with individual medications in the A to Z of antiretroviral medications.
If you feel uncomfortable mentioning your HIV medicine in a pharmacy, you could write the name of the drugs down and hand it to the pharmacist, or you could ask to speak to the pharmacist in a private consultation room. If you do need to mention the name of your HIV medicines, it’s very unlikely that anyone around you will recognise what they are used to treat.
It’s best to always go to the same high-street chemist. This will mean that your prescription records are in the same place, allowing the pharmacist to check for potential drug interactions.
Different types of HIV medicines
Some types of HIV medicines that belong to the drug classes protease inhibitors (PIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs) may be more likely to cause drug interactions compared to others. Some studies have shown a reduction in drug interactions when people switch from a protease inhibitor-based regimen to an integrase inhibitor-based regimen.
Protease inhibitor-based regimens often include ritonavir or cobicistat, which are boosting agents, taken to boost levels of the PI. The boosting agent may also have the effect of making other medicines stay in the body for longer or at higher levels. The boosting agent cobicistat is also included in combinations containing elvitegravir, which is an integrase inhibitor.
Erectile dysfunction drugs
If your HIV medicine includes ritonavir or cobicistat you should not take avanafil (Spedra or Stendra). You may still be able to take other erectile dysfunction medication, such as sildenafil (Viagra), tadalafil (Cialis), or vardenafil (Levitra), but you might need to take a lower dose. See our page on erectile dysfunction for more information.
Recreational drugs
There are potential interactions between some recreational drugs (for example, ketamine, ecstasy and crystal meth) and some NNRTIs and PIs. If you use recreational drugs, it is sensible to discuss this with your doctor, HIV pharmacist or other healthcare provider. See our page on interactions with recreational drugs for more information.
Gender-affirming hormone therapy
Some HIV medicines can interact with gender-affirming hormone therapy, although not all interactions are clinically significant. The European AIDS Clinical Society's guidelines include recommendations for dose changes in hormone therapy.
Herbal/alternative treatments
St John’s wort, a herbal remedy used to treat anxiety and depression, lowers blood levels of NNRTIs and PIs. It can cause them not to work effectively and there’s a risk of developing resistance.
In many cases, the interactions are theoretical, or seen in test-tube studies, and more information is needed about the likelihood of a real-life effect. For example, test-tube studies have indicated that African potato and Sutherlandia may reduce levels of PIs, NNRTIs and maraviroc (Celsentri) in the body.
Inhalers and nasal spray
Interactions can also happen with medicines that are not taken by mouth. For example, ritonavir and cobicistat can interact with inhalers and nasal sprays containing fluticasone, budesonide, mometasone, or salmeterol (e.g. Flixotide, Flixonase, Pulmicort, Seretide, Serevent, Nasonex and Pirinase), used to treat asthma and hay fever, potentially causing serious side effects. Cetirizine (Piriteze, Benadryl One-A-Day, Zirtek and Pollenshield) is a safe antihistamine to take with anti-HIV medications and can be bought over the counter or prescribed by your GP.
Ageing and problems with medications
Studies have found high rates of medication problems, including having the wrong medications, wrong dosages, and risk for severe complications among older and elderly people with HIV.
As we get older, our bodies change and process medicines differently. The liver and kidneys may work more slowly, affecting the way a drug breaks down and is removed from the body. As a result of weight loss, decreased body fluid or increased fatty tissue, medicines and drugs may stay in the body longer and cause more severe side effects.
The more drugs a person takes, the more likely they are to experience drug-drug interactions, or other problems such as inappropriate drugs, dosing errors, and so on. Older people with HIV are more likely to be taking a lot of different medications at the same time, for HIV and other conditions they have.
Taking multiple drugs can also increase the risk for other adverse outcomes. For example, if you are taking several different medicines that can affect your brain and nervous system, you are much more likely to experience drowsiness, confusion or memory problems. This can lead to falls and accidents.
Annual medication review
It's very helpful to have an annual medication review. This could be done by the pharmacist at your HIV clinic, your community pharmacist, or one of your doctors. In the United Kingdom, the National Institute for Health and Care Excellence (NICE) recommends that people with long-term conditions and people taking multiple medications have regular reviews.
After a medication review, the pharmacist or doctor may recommend some changes, such as stopping a medicine that you no longer need, switching a medicine to a newer or better version, or reducing the number of times a day you need to take medicines. The review may show that there is a medicine which you need but have not been getting.
Especially if you are taking a lot of medicines at different times of the day, a pill box with compartments for the days of the week and times of the day may be useful. It may help you keep track of what you need to take. Your pharmacist can give you advice on other ways to help you maintain your adherence.
This project has been made possible with grant support from MSD. MSD has no editorial control or input into this project.