Prazosin after a cat’s urinary blockage: what the trial found

This is a research explanation, not an instruction to start or stop medicine. If your cat is struggling to pee or passing little or no urine, contact an emergency clinic. If a prescribed medicine concerns you, speak to the treating vet.

After a cat has been unblocked, owners naturally want to prevent another emergency. A medicine can have a plausible reason for use without having demonstrated that outcome. Prazosin is a useful example.

What the researchers tested

Hanson and colleagues compared seven days of prazosin with placebo after relief of a first urethral obstruction. Eighty male cats were randomized; 65 were analyzed. Investigators and owners were blinded, and follow-up included an owner call.

The difference was not statistically significant (P = 0.27). This trial did not demonstrate prevention of repeat blockage. The higher percentage with prazosin also does not prove that it caused reblocking. Hanson et al., 2021.

Limits that matter

Twelve cats were excluded for not receiving the full medication course. Exclusions after randomization and small final groups limit confidence. Cats with radiographically identified bladder stones were ineligible, so the result cannot represent every obstructed cat or treatment regimen.

How it fits with other evidence

A separate 2017 randomized, blinded study involving 47 male cats also did not find a clear difference in repeat obstruction or owner-reported urinary signs with prazosin. Its authors explicitly cautioned that the study was underpowered. That means its size limited its ability to detect a difference; it does not mean the treatments were proved equivalent. Reineke et al., 2017.

The 2025 iCatCare consensus guideline says prazosin is not generally recommended on current evidence, while acknowledging remaining questions about possible subgroups and differences between study protocols.

A 2022 observational survey found a different association with recurrence. Its abstract describes veterinarians recruited by their always/never prescribing practice. It does not establish the explanation that difficult cases were selectively prescribed prazosin; confounding direction remains uncertain until fuller methods are checked. Association does not establish that the drug caused harm. Source 31, original abstract.

What an owner can take to the appointment

Ask: “What is this medicine intended to achieve for my cat, what evidence supports that aim, and what should I monitor?” A clinician may be making a decision about a specific patient that this short review cannot assess.

Also ask for clear return instructions. Repeat obstruction remains an emergency after discharge; a medication schedule should never become a reason to wait when urine output is uncertain. Animal Medical Center.

Why MSRA includes negative results

For this library, a useful paper is one that changes the clarity of a decision. Trials that fail to establish a benefit help identify where a reassuring story has outrun its evidence. We apply the same standard to future MSRA research.

MSRA paper-analysis draft. Sources checked 29 October 2026; not independently veterinary reviewed. This study was conducted by its named investigators, not by MSRA. Dosing instructions have intentionally not been reproduced.