Pharmacodynamics and Pharmacokinetics

When an individual assumes a substance it influences them, but at the same time they also influence the substance. The duration and the type of effect of a drug, pharmacodynamics, is related to the change of its concentration in the body over time, pharmacokinetics.
This concentration can be heavily influenced by the individual (Individual variability) as well as other substances in the bloodstream.

Some interactions between drugs may increase or decrease the expected effect by a certain sustance. In some cases the interactions are planned (Replacment therapy), and are sought to ehance the effect. In many cases, however, are not planned or expected, and the adverse consequences are often disastrous and sometimes fatal.

The ineractions may be predictable, repeatable or “random” and only occur in isolated instances.


Substances which acidify (eg. Raspberry juice) or alkalize (eg. Bicarbonate) in the urine, ie. substances which alter the pH, influence the pharmacokinetics of amphetamines due to the fact that the speed of their elimination is higher when urine is acidic and less when the urine is basic.
this procedure is desired and is generally used to influence the analysis of urine.

LSD + Antidepressants

It has been repeatedly reported that the phenomenon of “flashback” of LSD among adolescents is produced when they recieve antidepressant therapies based on inhibitors “uptake” of seratonin (ie. Paroxatine).

Chronic use of tricyclic antidepressants (eg. Prozac) is reported to increase physical, psychological and hallucinatory responses to LSD.

cannabis and alcohol

Controlled studies have reported that combining the use of these substances causes a degree of “disability” higher than that caused by the individual substances. It was, however, noted that the diability had largely disappeared by the following day.

Cocaine and alcohol

This type of reaction is unique. The combination of these sustances in the organism leads to the formation of a new substance called cocaethylene. This compound is formed only when the two substances are used together. Although it is known that the rate of elimination of such a compound is slower than that of the substances’ parents, its importance in the organism remains unclear if not only for analytical puposes.

Opioid Analgesics

Antibiotics are frequently used in patients undergoing medical or surgical procedures and quite often antibiotics interfere with the opioid analgesic used for treatment.
The best known are those with Erthromycin (which produces an increase in the action of opiates) and Riampicin (which produces a decrease).
Another interaction you have, are those drugs used in the treatment of epilepsy, particularly Carbamazepine, Phenytoin and barbiturates that increase the rate of metabalization of opioids in the liver.
Even the tricyclic antidepressants Clomipramine and amitryptyline significantly increase the plasma availability for morphine.
One of the more “violent” interactions with opiates we see in the case of “rapid detoxification”when a small amount of of Naloxone (0.5g), is injected into addicts .This reaction brings on a syndrome very similar to withdrawls from opiates but, with the difference being it starts in a few minutes and passes within a few hours.

Drugs and Depression

The combining of certain drugs like alcohol and heroin or alcohol and tranquilizers, which are some of the most common interactions, are some of the most dangerous because the effects of one amplifies the other.
Alcohol is probably the most common “mixer”. Infact a large portion of the deaths from overdose of heroin also involve the presence of alcohol. Similarly, pharmacological barbiturates can easily become lethal when mixed with alcohol.