Treatment training manual

3.15 Adherence – and why it is so important

What is adherence?

Adherence means taking your drugs exactly as prescribed.

  • This includes taking them at roughly the right time each day.
  • It also includes following any restrictions about taking them with or without food.

This will make sure that each drug stays at the level needed to fight HIV.

Drug levels need to stay above this minimum 24 hours a day, 7 days a week, 365 days a year. Every time drug levels fall too low there is a chance of drug resistance.

Regular doses means safe drug levels that keep HIV under control

  • Getting into a good routine will help you remember your meds.
  • Oral ART involves a daily schedule and adherence can be difficult. You may need some support to get used to the changes it makes in your life.
  • Good adherence is the most important thing you have to think about when you start a new combination.
  • Start ART when you can give yourself the extra time and space you may need to adjust.
  • During the first few weeks, nothing else should take priority over getting your treatment right.

Some HIV clinics have an adherence clinic or a nurse who can help.

Although taking medication on time is important, there is always a window period of about an hour either is still okay. Some drugs, and some people, have a wider window period than others.

Because of this variation, it is still better to aim for roughly the same time each day.

It is important to follow advice about whether your meds need to be taken with or without food. Ignoring this can be like only taking half a dose or taking a double-dose. You will notget the right drug levels for it to work.

How much adherence is enough?

Many people want to know how exact they need to be?

This is about both timing of dosing and missing doses.

When starting ART, the answer is to try to not miss doses and to try to take every dose at roughly the same time. Everyone is still likely to miss an odd dose and this will be okay. There is also a window od 1-2 hours either side of the ideal time. The main aim is to get into a good routine that will help you afterwards.

Once you are undetectable, there can be a bit more flexibility. The window to take your meds might be a few more hours either side of the ideal time. Some studies show that once you are undetectable, missing odd doses is also okay,

This is really so that you don’t worry too much if this happens. But the benefit of aiming for roughly the same time is that you will get into a good routine.

Taking your meds as prescribed gives you the best chance of good results.

  • Work out how adherent you are through a regular week.
  • Be strict with yourself when monitoring your adherence.
  • If it’s not so good, ask for more support. You will need to ask.
  • Talk to your doctor!

Are some combinations more flexible?

Whatever your combination and treatment history, the best adherence will give you the best results.

This is especially true when starting ART until viral load becomes undetectable.

Most once-daily oral combinations are just as good at covering for od missed doses.

If any of your meds need to be taken twice-daily, adherence needs to be more careful.

Some studies have also reported that missing one or two doses a week might also be okay, but not others. [1, 2]

Learning support module — What happens when you take a drug

Learning support module — Drug levels, drug activity and side effects


  1. Cohen C et al. The FOTO study: The 48 week extension to assess durability of the strategy of taking efavirenz, tenofovir and emtricitabine five days on, two days off (FOTO) each week in virologically suppressed patients. (Poster abstract MoPeB063.) Paper presented at the Fifth IAS Conference on HIV Pathogenesis, Treatment, and Prevention, 19–22 July 2009, Cape Town, South Africa.
  2. Four days on, three days off is NOT as effective as daily ART: French study results need to be interpreted with caution. HTB (August 2019).

Last updated: 1 January 2023.