Options for providing analgesia to cats outside of a veterinary hospital are limited. Currently, these options are: oral non-steroidal anti-inflammatory drugs (NSAIDs), tramadol, transdermal fentanyl, and transmucosal buprenorphine. NSAIDs have a high risk for toxicity in cats, and no drug is labeled in the United States for repeated administration in cats. Opioids are often considered as the first line of treatment for acute pain. Unfortunately, they are expected to have a short duration of action after oral administration, because of the so-called first-pass effect Indeed, absorption through the gastrointestinal system results in delivery of the drug to the liver, which inactivates a large fraction of the drug. An alternative of clinical interest is absorption through the buccal mucosa. Injectable buprenorphine has been reported to be well absorbed after administration in cats’ mouth and to result in good analgesic efficacy, yet recently buprenorphine has been in limited supply. The proposed study will look at transmucosal absorption and analgesic efficacy of four other opioids—oxymorphone, hydromorphone, methadone, and morphine—in cats. The information should be important for all veterinarians when they must provide short term or long term analgesia to cats and may confront shortages, deleterious effects, or a lack of efficacy related to other drugs.