Many people treat dietary supplements as completely safe products that can be freely combined with each other and with medications they take. This is one of the most common and most underestimated mistakes in supplementation.
The fact that a given product is available without a prescription does not mean it has no effect on the body. In reality, many active substances found in supplements influence drug metabolism, the activity of biological systems, and the absorption of nutrients and pharmaceuticals.
Interactions can lead to weakened drug effects, intensified side effects, lack of therapeutic efficacy, and in extreme cases even severe health complications and death.
Interactions (in broad simplification) can be divided into three main levels:
1. Metabolic interactions
These are interactions that occur at the level of metabolism of active substances - most often in the liver. Enzymes from the cytochrome P450 (CYP450) family play a key role here, as they are responsible for breaking down a huge number of drugs and bioactive substances.
If a supplement inhibits the activity of a specific enzyme, a drug metabolized through the same pathway will be broken down more slowly. As a result, its blood concentration may rise to levels that cause adverse effects or even toxicity.
A good example is berberine, which inhibits the activity of CYP2D6 and CYP3A4 enzymes. If a person simultaneously uses drugs metabolized through these pathways, e.g. certain beta-blockers, their concentration in the body may increase. The result may be excessive lowering of blood pressure, dizziness, weakness, or heart rhythm disturbances.
Other examples:
- Grapefruit juice (or extract) inhibits the CYP3A4 isoform, which can increase the concentration of many cardiovascular, immunosuppressive, or psychiatric drugs.
- St. John's wort (extract) works in the opposite way and stimulates the activity of certain CYP450 enzymes and the P-gp transporter (P-glycoprotein), accelerating the metabolism of many drugs. As a result, it can weaken the effect of hormonal contraception, antiepileptic drugs, or immunomodulating agents, among others.
In practice, this means that even effectively managed pharmacotherapy can be disrupted by a seemingly harmless supplement.
2. Mechanistic interactions
At this level, the problem is not metabolism but the mechanism of action of the substances themselves. They can mutually enhance their effects (synergy) or act in opposition (antagonism).
Dangerous synergy - the serotonergic system
A classic example is combining antidepressants from the SSRI, SNRI, or MAO inhibitor groups with supplements that affect serotonin levels in the brain.
Such supplements include, among others:
- Kanna (Sceletium tortuosum),
- St. John's wort,
- 5-HTP,
- SAMe (S-adenosyl-L-methionine),
- and to a lesser extent also some adaptogens and plant extracts.
Each of these substances increases the activity of the serotonergic system. Combining them with antidepressants can lead to excessive stimulation of serotonin receptors and the development of serotonin syndrome, which is a life-threatening condition.
The same applies to combining them with each other - e.g. Kanna + St. John's wort (extract) can also cause the same negative serotonergic effect.
Antagonism - opposing action
Another problem is a situation in which a supplement acts opposite to the goal of therapy.
An example may be glucocorticosteroids used as immunosuppressive drugs in certain autoimmune diseases or after transplants. Their purpose is to weaken immune system activity.
Simultaneous use of immunostimulating substances, such as beta-glucans, can partially cancel out the intended therapeutic effect. Although the clinical significance depends on the specific situation, this is an example of an interaction that can work in the opposite direction to the assumptions of treatment.
3. Absorption interactions
The third level concerns the absorption of substances from the gastrointestinal tract.
Some supplements can bind drugs in the intestinal lumen or make it harder for them to contact the mucous membrane, thereby reducing the amount of substance entering the bloodstream.
Great examples include, among others:
- Inulin
- Guar gum
- Chitosan
If taken at the same time as drugs or other supplements (e.g. minerals), they can limit their absorption and reduce the effectiveness of therapy.
- Curcumin also inhibits gastrin secretion (the hormone that stimulates the stomach to produce hydrochloric acid HCl) - by raising the overall pH of gastric juice - indirectly reducing the reduction of non-heme iron to heme iron, thereby making its absorption from the gastrointestinal tract into the blood more difficult.
The phenomenon of inhibiting absorption of active substances also works the other way around. Some drugs or pharmacological substances can limit the absorption of supplement ingredients.
Examples:
- Lactulose accelerates intestinal transit and potentially reduces the contact time of certain ingredients with the intestinal mucosa,
- Activated charcoal absorbs numerous compounds present in the gastrointestinal tract, including active substances from supplements.
As a result, weaker absorption of herbal extracts, vitamins, or other bioactive components may occur.
Summary
When planning supplementation, it is worth looking not only at the potential benefits of individual ingredients, but also at their mutual interactions and impact on medications being used.
Interactions can occur at the level of:
- Metabolism (CYP450 enzymes),
- Mechanism of action (synergy or antagonism),
- Absorption from the gastrointestinal tract.
Ignoring these relationships can lead to a situation in which supplementation becomes completely ineffective and pharmacotherapy stops working as intended.
In the best case, this ends with a placebo effect and wasted money. In the worst case - loss of health, severe adverse effects, and even a threat to life.
Therefore, every extended supplementation plan should be analyzed not only for potential benefits, but also for possible interactions.
At NutriLogic, we take interactions into account at all three levels (and much more) with more than 3000 active substances found in drugs available in Europe, North America, and Asia.
We know that effectiveness is the measure of truth, but safety is what matters most.
~ NutriLogic Science Team