Some pets slow down in summer. But if your dog can’t handle the heat or your cat becomes unusually lethargic, it may be more than just warm weather. Hidden metabolic conditions can affect how pets respond to heat—and getting a proper diagnosis could make all the difference.

"He Just Can’t Handle the Heat"

If your pet pants excessively, avoids activity, or seems weak after minimal exertion, it may not just be the temperature. These can be signs of underlying conditions like:

• Hypothyroidism: Slows metabolism and energy

  • Hypothyroidism is a condition where the thyroid gland doesn’t produce enough thyroid hormone. This hormone is essential for regulating metabolism, so when levels are low, pets can experience fatigue, weight gain, poor coat quality, and a decreased ability to regulate body temperature. Dogs with hypothyroidism often appear sluggish, tire easily, and may struggle to stay cool in warm weather due to slowed metabolic function.

• Diabetes Mellitus: Impacts hydration, energy, and overall health

  • Diabetes occurs when the body can’t properly regulate blood sugar levels, typically due to insulin deficiency or resistance. This leads to symptoms like increased thirst, frequent urination, weight loss, and fatigue. In the heat, these symptoms can be even more noticeable—dehydration happens faster, and energy levels drop more dramatically. Unmanaged diabetes can also impair a pet’s ability to handle environmental stress, making heat tolerance worse.

• Addison’s Disease: Reduces stress hormone production, affecting the body’s ability to adapt to heat or exertion

  • Addison’s disease affects the adrenal glands, which produce hormones like cortisol that help the body respond to stress. In pets with Addison’s, these hormones are lacking, which can lead to episodes of weakness, vomiting, diarrhea, and collapse, especially during times of heat, excitement, or physical exertion. Because their bodies can’t mount a normal stress response, pets with Addison’s often struggle more in hot weather and may seem especially fatigued or unwell.

Not Just a Hot Day: What Heat Intolerance Really Looks Like

Heat intolerance isn’t just discomfort—it can involve serious symptoms like:

• Muscle weakness or shaking

• Vomiting or diarrhea

• Sudden collapse or disorientation. If your pet shows these signs consistently, especially in warm weather, it’s time to look deeper.

Thyroid & Adrenal Health in Pets

Endocrine glands like the thyroid and adrenal glands regulate key functions like metabolism, energy, and fluid balance. Internists at VSH North County use targeted hormone testing, advanced lab panels, CT imaging, and collaborative evaluations with other specialists to catch issues that regular exams may miss.

Hydration Isn’t Always Enough

If your pet is drinking plenty of water but still seems tired or distressed, it may point to an underlying medical issue. Internal Medicine specialists know when it’s more than just hydration and can guide you toward answers.

Summer-Specific Warning Signs

Know what’s normal and what’s not. Watch for:

• Excessive panting

• Lethargy not resolved by rest

• Reduced appetite

• Unusual GI symptoms in warm weather

At VSH North County, our Internal Medicine team combines cutting-edge diagnostics with a deeply compassionate approach. If you think your pet isn’t handling the heat like they used to, we’re here to uncover the cause and help them get back to feeling their best.