Types of drug interaction

When two or more different drugs are taken together, an effect other than that achieved with each single drug may result. This is also true of drug side-effects. For example, taking two drugs that each cause peripheral neuropathy increases the likelihood of the occurrence of neuropathy.

It is not only prescribed medicines that can interact. The presence of food in the stomach can increase or decrease the absorption of drugs. There may also be interactions between prescribed medicines and recreational drugs or complementary therapies, although these are often poorly researched.

Drug interactions are usually divided into four groups: antagonism, synergism, potentiation, and interaction with metabolism.

Antagonism means that one drug reduces or blocks the effect of another. There are various ways in which this can happen. For instance, drugs can interfere with each other's absorption in the gut, circulation in the blood, or uptake by cells.

Synergism means that two or more drugs work together against one target, producing an effect that is greater than the individual effect of the two drugs together (like combining two plus two and getting five). Synergistic interactions can be beneficial and treatments may be deliberately chosen for this effect. 

Potentiation means that drug A boosts the effects of drug B, often by increasing the levels of drug B in the blood. Like synergism, this may be useful in cases in which the beneficial effects of drug B are enhanced. However, the toxicities of drug B may also be potentiated, leading to an increased level of side-effects.

Community Consensus Statement on Access to HIV Treatment and its Use for Prevention

Together, we can make it happen

We can end HIV soon if people have equal access to HIV drugs as treatment and as PrEP, and have free choice over whether to take them.

Launched today, the Community Consensus Statement is a basic set of principles aimed at making sure that happens.

The Community Consensus Statement is a joint initiative of AVAC, EATG, MSMGF, GNP+, HIV i-Base, the International HIV/AIDS Alliance, ITPC and NAM/aidsmap

This content was checked for accuracy at the time it was written. It may have been superseded by more recent developments. NAM recommends checking whether this is the most current information when making decisions that may affect your health.

NAM’s information is intended to support, rather than replace, consultation with a healthcare professional. Talk to your doctor or another member of your healthcare team for advice tailored to your situation.