I do not have the in-depth knowledge so I figured I'd seek some answers from the professionals.

Drugs or medicine often inhibit a certain hormone or action within the human body to treat a symptom such as, dopamine antagonist or ACE inhibitors. Since the drug restricts what would have been 'normal' to its usual standards but not normal to the healthy standards, would inhibitors be more likely to cause side effects to a human being in general or only drugs targeting specific parts that are likely to cause side effects.

I’m not sure that I quite understand your question! If we take dopamine as an example, this catecholamine binds to 5 subtypes of receptors, D1-5. These 5 receptors are structurally very similar but have different pharmacological profiles, i.e., they are all activated by the endogenous ligand dopamine but they bind different exogenous antagonists and agonists with different affinities. Subtype-specific antagonists may bind to different places in the D receptor(s). The D receptors also have different tissue distributions, although these may overlap in various places, e.g., in a brain region involved in reward called the striatum. As far as I am aware no D receptor is restricted to one tissue (there are few genes that are truly tissue-specific), so in theory a general antagonist to D1-5 would block dopamine function in multiple tissues, as would a specific antagonist against one D receptor subtype. This can give rise to side-effects in one or more tissues that may be detrimental in terms of therapeutic treatment, or may be well-tolerated. Side-effects may also arise, e.g., if the D receptors are functionally complexed to different proteins that have different (non-dopamine) functions, or if the D receptors are an intermediate in a (non-dopamine) physiological pathway. Please post again if you need further clarification.

Last edited by Steve Lolait (13th Nov 2015 09:26:56)

i too was unclear what Tom was asking. An additional point to note, most if not all drugs cause side effects that are on- and off-target. The former is a side effect by altering the activity of the target the drug works at eg a receptor in the brain is also expressed in the gut - antagonising the brain action also antagonises the gut which causes for example nausea or diarrhoea. Off target is when the drugs acts at other target all togeher and thus may affect unexpectedly other systems eg kidney or liver.

As Steve says, please do post again if we haven't answered your question.