If you take blood-pressure medication, the supplements worth thinking about are the ones that lower blood pressure on their own, plus one mineral that needs a closer look on certain drugs. Most blood-pressure medicines fall into a few families: ACE inhibitors like ramipril and lisinopril, ARBs, beta-blockers like bisoprolol, and calcium channel blockers like amlodipine. The supplement questions are similar across all of them.
Supplements that also lower blood pressure
Several supplements have a mild blood-pressure-lowering effect of their own: magnesium, garlic extract, hibiscus, CoQ10 and beetroot or nitrate supplements. On a well-controlled regimen these can be a useful nudge. The thing to watch is the opposite problem: if your blood pressure already runs toward the low end on your medication, adding one of these can tip you into dizziness or light-headedness on standing. It is not dangerous so much as worth introducing one at a time and paying attention to how you feel.
The one that needs monitoring: potassium
ACE inhibitors and ARBs both raise potassium as part of how they work. That makes a potassium supplement, or a "low-sodium" salt substitute that is mostly potassium, something to be careful with on these drugs, because pushing potassium too high carries its own heart risk. If you take an ACE inhibitor or ARB, a potassium supplement is one to clear with your GP and monitor with a blood test rather than start on your own.
The simple version
Treat BP-lowering supplements as additive: helpful when your control has room, risky when it is already at the low end, and best introduced one at a time. Be cautious with potassium on an ACE inhibitor or ARB. To check a specific supplement against your blood-pressure medication, the free checker will show you the call and the reasoning. If your interest is partly about energy or tiredness, it is worth ruling out the simple causes covered in the B12 and iron territory first.