Lacking a concrete example in the question that clearly gives the original context for (a one time) usage, this answer is supplementing the other answers along the findings a general net search for this specific word and its usage reveals.
Literally, a Medikamentenversuch is a neutral word describing a clinical drug trial, also and especially in humans.
These trials are in principle: necessary for approval of a drug, now strongly regulated, with oversight from ethics commissions for example, tightly controlled for adverse outcomes, and ended prematurely if necessary.
In actual usage, most commonly found in search results, this compound word is constructed and used like the category parent word Menschenversuch (according to Wikipedia: ~"Human subject research") Both those -versuche are originally not describing anything unethical or illegal. Although both are neutral in their original meaning they are overwhelmingly used to describe violations of ethical research standards. That means drug trials where for example no informed consent was given, the dangers involved in every human trial were obviously too high, test subjects were tested to their limits and beyond etc. Sometimes severe side effects, among them them simple death were commonly accepted – by those conducting the trials (Example: Nazi human experimentation). In hindsight, or when these deeds came to the light of the public these type of trials are almost universally condemned and reported as major scandals in medicine in recent years. In such cases, most writers seem to exclusively choose Menschenversuche or Medikamentenversuche to name and blame the experiments, whereas constructions like klinische Studien or Versuche am Menschen are chosen if they talk about proper trials, conducted according to accepted standards.
This narrower and strongly negatively connotated meaning in actual usage can be shown in several ways:
If you use an evil search engine and look for "Medikamentenversuche", or "Menschenversuche", then it displays almost exclusively scandals in medicine and reports relating to trials of a different kind: court trials, sentences and so on. Again: it seems that "klinische Studien", "Versuche am Menschen" are used to report legal and ethically less problematic, scientifically deemed necessary trials. (Although they might have there own kinds of problems and scandals, like in studying TGN1412).
This can be shown also with more focus on medicine. It is not just yellow press word usage. Use the internal search engine of for example
Ärzteblatt, a newspaper for doctors.
This empirical evidence of Sprachpraxis is quintessentially demonstrated in the following article: Geschichte der Medizin – Ansichten zur Ethik: Menschenversuch und Menschlichkeit
What does “Medikamentenversuche” mean or refer to?
It means: Medikamentenversuche can therefor be simple (human) drug trials, according to accepted standards, perfectly legal – and necessary. In theory, this is the original, broad, and intended meaning of the word by itself.
–or, more commonly in daily usage–
It most often refers to: Medikamentenversuche is overwhelmingly used to denote criminal, unethical "research", sometimes outright pseudoscientific experiments, with drugs, on humans. Illegal, improper, unethical "trials", medical scandals. In practice this is the context in which the word is most often found.
(If the the test subject isn't human, the term Tierversuch is used by similar critics and proponents of action against for all kinds of unethical behaviour against animals.)