This does not work on compounds sensitive to stomach acids. Some medications (both veterinarian and human) have to be specially coated to survive this environment [1], if you crush the pills the medication gets less effective, completely ineffective or, like ibuprofen, irritate the stomach. Or, worst case, the medication is designed for retarded release in the stomach acid - and now that you've crushed it, the entirety of the compound is dissolved in the stomach at once.

Please always ask your veterinarian/physician, the pharmacy staff and always read the medication's application notes because particularly physicians often are unaware and the same ingredient on the prescription might be fulfilled by a crushable or a non-crushable variant which only the pharmacist knows.

[1] https://de.wikipedia.org/wiki/Magensaftresistente_Tablette