This study is for people aged 18 to 80 who have **difficult-to-control high blood pressure** (hypertension). It's testing a new medicine called **MANP**, which is given as a shot under the skin. The medicine's effects are compared to a **placebo** (a "sugar pill" that doesn't have any active medicine). Participants must already be taking at least three blood pressure pills that work in different ways. One of these pills must be a **diuretic** (a pill that helps your body get rid of extra fluid) and another must be an **ACE inhibitor** or **ARB** (both help relax blood vessels). **Blood pressure** (SBP) should be high despite these medications. Some people with a kidney condition called CKD can also join if their kidney function is above a certain level. **Key Points:** - The study involves subcutaneous injections and regular blood pressure monitoring. - Participants must be on specific blood pressure medications and have certain health conditions. - People with severe health issues like heart failure or recent heart attacks cannot join. This study helps researchers learn if MANP can safely lower blood pressure better than current treatments.