What Side Effects Should You Expect With Relexxii?

Relexxii (methylphenidate hydrochloride extended-release) is a Schedule II CNS stimulant prescribed for ADHD in adults and children ages 6 and older. Like all stimulant medications, it comes with a range of possible side effects — some mild and manageable, others that require immediate medical attention.

This guide breaks down the most common Relexxii side effects, the serious ones you need to watch for, which populations face higher risks, and practical tips for managing symptoms while staying on treatment.

Common Side Effects of Relexxii

Most people who take Relexxii experience at least one or two side effects, especially during the first few weeks of treatment or after a dose increase. These are generally mild and tend to improve as your body adjusts:

• Decreased appetite — The most frequently reported side effect. Many patients notice they simply aren't hungry, especially during the hours the medication is active.
• Headache — Common in both adults and children starting Relexxii.
• Dry mouth — Stimulants can reduce saliva production.
• Nausea — Often worse on an empty stomach.
• Insomnia — Difficulty falling asleep, especially if the medication is taken too late in the day.
• Anxiety — Some patients feel more on edge or jittery.
• Dizziness — Usually mild and temporary.
• Weight loss — Often related to appetite suppression over time.
• Irritability — More common in pediatric patients.
• Increased sweating — Particularly during physical activity.
• Upper abdominal pain — Reported more frequently in children.

If these side effects persist beyond the first few weeks or significantly affect your quality of life, talk to your prescriber. A dose adjustment or timing change can often help.

Serious Side Effects: When to Call Your Doctor Immediately

While uncommon, Relexxii can cause serious side effects that require prompt medical attention. Contact your doctor right away — or call 911 — if you experience any of the following:

Cardiovascular Events

Relexxii can increase blood pressure and heart rate. In rare cases, stimulant medications have been associated with sudden death, stroke, and heart attack, particularly in patients with preexisting heart conditions. Watch for:

• Chest pain or tightness
• Shortness of breath
• Fainting or feeling like you might pass out
• Rapid or irregular heartbeat

Your doctor should check your heart rate and blood pressure before starting Relexxii and at regular follow-up visits.

Psychiatric Symptoms

Stimulants can trigger or worsen psychiatric symptoms, even in patients without a prior history. Be alert for:

• New or worsening psychosis (seeing or hearing things that aren't there)
• Mania or manic episodes
• Significant aggression or hostility
• Severe anxiety or panic attacks

Priapism

Prolonged and painful erections have been reported with methylphenidate products, including Relexxii. This is a medical emergency — seek immediate help if an erection lasts more than four hours.

Peripheral Vasculopathy (Raynaud's Phenomenon)

Relexxii may cause circulation problems in the fingers and toes, resulting in:

• Numbness or tingling
• Fingers or toes turning white, blue, or red
• Unexplained pain in the extremities
• Sensitivity to cold temperatures

Serotonin Syndrome

If you take Relexxii alongside serotonergic medications (such as SSRIs, SNRIs, or triptans), there's a risk of serotonin syndrome — a potentially life-threatening condition. Symptoms include:

• Agitation or restlessness
• Rapid heartbeat
• Muscle twitching or rigidity
• High fever
• Diarrhea

If you suspect serotonin syndrome, seek emergency medical care immediately.

Gastrointestinal Obstruction

Relexxii uses an osmotic delivery system — the tablet doesn't dissolve like a normal pill. Instead, the non-digestible shell passes through your GI tract intact (you may notice it in your stool, which is normal). However, patients with severe gastrointestinal narrowing should not take Relexxii, as the rigid tablet could cause a blockage. This includes patients with esophageal motility disorders, small bowel inflammatory disease, short gut syndrome, or a history of peritonitis.

Side Effects by Population

Children and Adolescents (Ages 6-17)

Pediatric patients may be more likely to experience:

• Appetite suppression and associated weight loss
• Upper abdominal pain
• Irritability and mood changes
• Growth suppression — Long-term stimulant use may slow height and weight gain in children. Your child's doctor should monitor growth regularly and may recommend drug holidays during school breaks to allow catch-up growth.

Adults

Adults tend to report more:

• Dry mouth
• Insomnia
• Anxiety
• Increased sweating

Older Adults (Over 65)

Relexxii has not been extensively studied in patients over 65. If you're in this age group, your doctor should exercise extra caution, particularly regarding cardiovascular monitoring.

Pregnant and Breastfeeding Patients

Relexxii should only be used during pregnancy if the potential benefits outweigh the risks. Methylphenidate is present in breast milk, so breastfeeding patients should discuss the risks with their provider.

How to Manage Common Side Effects

Many Relexxii side effects can be minimized with simple adjustments:

For Decreased Appetite and Weight Loss

• Eat a substantial breakfast before the medication kicks in
• Have a larger dinner after the medication wears off
• Keep calorie-dense snacks available throughout the day
• Set meal reminders on your phone — stimulants can make you forget to eat

For Insomnia

• Take Relexxii first thing in the morning — never in the afternoon or evening
• Establish a consistent bedtime routine
• Avoid caffeine, especially after noon
• Talk to your doctor about dose timing or a possible dose reduction

For Headache

• Stay well hydrated
• Eat regular meals (low blood sugar can compound stimulant headaches)
• Over-the-counter pain relievers like acetaminophen are generally safe, but check with your pharmacist

For Nausea

• Take Relexxii with food — it can be taken with or without meals, but food often helps
• Avoid greasy or heavy foods around dosing time
• Start at a lower dose and titrate up slowly if nausea is persistent

For Dry Mouth

• Sip water frequently throughout the day
• Chew sugar-free gum to stimulate saliva
• Avoid alcohol-based mouthwashes

For Anxiety or Jitteriness

• A lower dose may provide ADHD symptom relief with less anxiety
• Limit caffeine intake, as it can amplify stimulant-related anxiety
• Practice relaxation techniques like deep breathing
• If anxiety is significant, talk to your doctor — it may indicate the dose is too high or that a different medication would be a better fit

The Boxed Warning: Abuse and Dependence

Relexxii carries a boxed warning (the FDA's most serious warning) about the potential for abuse and dependence. Methylphenidate is a Schedule II controlled substance, the same category as medications like Adderall and OxyContin. This means:

• Your doctor should assess your risk of substance abuse before prescribing
• You should take Relexxii exactly as prescribed — never take more than your prescribed dose
• Do not share your medication with others
• Your doctor should monitor for signs of misuse during treatment

When taken as prescribed for ADHD, the risk of developing a substance use disorder from Relexxii is considered low. However, the warning exists because misuse at higher doses can lead to dependence.

When to Talk to Your Doctor vs. When to Go to the ER

Here's a quick reference:

Schedule a call or visit with your doctor if you notice:

• Persistent appetite loss causing significant weight loss
• Insomnia that doesn't improve with timing adjustments
• Mood changes, increased irritability, or mild anxiety
• Headaches that don't respond to basic remedies
• Circulation changes in fingers or toes (mild)

Go to the emergency room or call 911 if you experience:

• Chest pain, irregular heartbeat, or shortness of breath
• Signs of a stroke (sudden weakness, confusion, trouble speaking)
• Hallucinations, delusions, or severe paranoia
• Prolonged erection lasting more than 4 hours
• Signs of serotonin syndrome (high fever, muscle rigidity, agitation)
• Severe allergic reaction (hives, swelling, difficulty breathing)

Final Thoughts

Side effects are a normal part of starting any new medication, and Relexxii is no exception. Most common side effects are mild and improve with time or simple adjustments. The serious ones are rare but important to know about so you can act quickly if they occur.

The manufacturer of Relexxii has partnered with Medfinder to provide medication locating services free of charge. Visit medfinder.com to find Relexxii in stock near you at no cost.

Thanks to a partnership between Relexxii's manufacturer and Medfinder, you can use Medfinder's medication locating services completely free of charge.

The most important thing you can do is stay in communication with your prescriber. Don't tough it out in silence — and don't stop taking Relexxii abruptly without medical guidance.

For more on how Relexxii works and whether it's the right fit for your ADHD, read our guide: What Is Relexxii? Uses, Dosage, and What You Need to Know in 2026. And if you're having trouble finding Relexxii in stock at your pharmacy, Medfinder can help you check pharmacy availability in seconds.