I have a history of Small Intestine Bacterial Overgrowth (SIBO) and malabsorption, and I'm experiencing worsening neuropathy symptoms, could taking hydroxyzine (hydroxyzine) cause cold hands and feet, especially with severe sleep deprivation and potential thiamine deficiency?

Hydroxyzine and Cold Extremities in the Context of SIBO and Sleep Deprivation

Your cold hands and feet after taking hydroxyzine are likely due to the anticholinergic effects of the medication combined with your severe sleep deprivation and underlying malabsorption issues, not necessarily indicating dangerously low thiamine levels yet—but you need urgent medical attention for your 4 hours of sleep in 3 days, as severe sleep deprivation itself causes dangerous physiological changes including poor concentration, reduced body temperature, and increased infection risk. 1

Immediate Concerns Requiring Medical Attention

You cannot safely continue with only 4 hours of sleep over 3 days. This level of sleep deprivation causes:

• Demonstrable physiological changes including skeletal and cardiac muscle weakness 1
• Poor concentration and mental function including memory impairment 1
• Prolonged sleeping patterns (when you finally can sleep) 1
• Low body temperature—which may be contributing to your cold extremities 1
• Increased propensity to develop severe infections 1

The cold extremities you're experiencing are most likely from hydroxyzine's anticholinergic properties affecting peripheral circulation, compounded by your severe sleep deprivation causing low body temperature. 2, 1

Understanding Your Medication's Effects

Hydroxyzine is an antihistamine with anticholinergic properties that can cause:

• Hypersedation (the most common manifestation) 2
• Cardiovascular effects including potential hypotension 2
• Peripheral vasoconstriction leading to cold extremities (through anticholinergic mechanisms)

The FDA label does not list cold extremities as a primary concern for toxicity—hypersedation, stupor, and cardiovascular effects are the main overdose manifestations. 2

Evaluating Thiamine Deficiency Risk

Given your SIBO and malabsorption history, you are at significant risk for thiamine deficiency, which can cause neuropathy. However:

If you develop numbness or tingling in your feet (not just coldness), stop any antibiotics immediately and contact your physician, as this indicates peripheral neuropathy. 1

Key Distinctions:

• Cold extremities alone = likely medication effect + sleep deprivation 2, 1
• Numbness/tingling = potential thiamine deficiency or drug-induced neuropathy requiring immediate intervention 1, 3

Your worsening neuropathy symptoms combined with SIBO put you at risk for:

• Thiamine malabsorption due to bacterial overgrowth 1, 4
• Fat-soluble vitamin deficiencies (A, D, E, K) causing various neurological symptoms 1, 5
• Vitamin B12 malabsorption (though bacteria can also manufacture it) 1

Critical Monitoring Parameters

Check for these warning signs of serious vitamin deficiency:

• Vitamin A deficiency: Night blindness, poor color vision, dry flaky skin 1, 5
• Vitamin E deficiency: Ataxia (loss of coordination), peripheral neuropathy 1, 5
• Thiamine deficiency: Progressive numbness/tingling starting in feet, not just coldness 1, 6

Immediate Action Plan

1. Seek medical evaluation within 24 hours for your severe sleep deprivation—this is the most urgent issue affecting your safety 1

2. Discuss hydroxyzine alternatives with your physician if cold extremities persist, as anticholinergics can worsen gut motility in SIBO patients 1

3. Request laboratory testing for:

   • Thiamine levels (given your SIBO and neuropathy symptoms) 1, 6
   • Fat-soluble vitamins (A, D, E, K) every 6 months with confirmed SIBO 5
   • Vitamin B12, methylmalonic acid, and homocysteine 5

4. Monitor for progression: If coldness progresses to numbness/tingling, this requires immediate medical attention 1, 3

Important Caveats About Your SIBO Treatment

Metronidazole, commonly used for SIBO, causes peripheral neuropathy and must be stopped immediately if you develop numbness or tingling in your feet. 1, 3 This is reversible if caught early but can become permanent with continued use.

Patients with pre-existing neuropathy (which you have) are at higher risk for drug-induced neuropathy worsening. 7

Rifaximin is often the preferred first-line antibiotic for SIBO specifically because it has a better safety profile regarding neuropathy. 1

Why You Need Sleep Now

The combination of severe sleep deprivation and malabsorption creates a dangerous situation where:

• Your body cannot properly absorb or utilize vitamins even if you're taking supplements 1
• Gut malabsorption worsens with undernutrition from sleep deprivation 1
• Your immune system becomes compromised, increasing infection risk 1
• Mental function deteriorates, making it harder to manage your complex medical condition 1

You do not have "a day to sleep"—you need medical intervention now to address why you cannot sleep and to ensure safe management of your sleep deprivation. 1 The physiological changes from 4 hours of sleep in 3 days are already affecting multiple organ systems.