Cats can have pistachios, but it is generally not recommended. Pistachios are not toxic to cats, so they are not inherently harmful if ingested in small amounts. However, they pose several health risks and are not suitable as a regular part of a cat's diet. The major concerns with feeding pistachios to cats include:

• High fat content in pistachios can lead to pancreatitis, a serious inflammation of the pancreas.
• Pistachios often contain salt or seasonings which can cause gastrointestinal upset and sodium toxicity in cats.
• The shells of pistachios can be a choking hazard or cause intestinal blockage if swallowed.
• Cats' digestive systems are not designed to process nuts well, leading to potential stomach upset, vomiting, diarrhea, and loss of appetite.
• Some cats might have allergic reactions to pistachios.
• Overconsumption can contribute to weight gain, kidney problems from oxalates, and other issues.

If a cat accidentally eats a plain, unshelled pistachio in very small quantity, it will likely be okay, but it is best to avoid feeding pistachios intentionally. Always keep pistachio shells away from cats to prevent choking or intestinal obstruction. If you notice symptoms like lethargy, vomiting, abdominal pain, or behavioral changes after ingesting pistachios, consult a veterinarian promptly. In summary, pistachios are not toxic, but they are not a safe or healthy treat for cats due to fat content, potential additives, and physical hazards from shells. It is safest to avoid giving pistachios to cats altogether and opt for treats formulated specifically for feline health.