What is the difference between monophasic, biphasic, and triphasic oral contraceptives?

Differences Between Monophasic, Biphasic, and Triphasic Oral Contraceptives

The main difference between monophasic, biphasic, and triphasic oral contraceptives is in their hormone dosing patterns: monophasic pills contain the same hormone dose throughout the cycle, while biphasic have two different dosing phases, and triphasic have three different hormone dosing phases designed to mimic the natural menstrual cycle. 1

Monophasic Oral Contraceptives

• Contain the same dose of estrogen and progestin in each active pill throughout the cycle
• Most commonly prescribed type of combined hormonal contraceptive
• Simpler formulation with consistent hormone levels
• Available in various estrogen doses (typically ≤50 μg of ethinylestradiol) combined with different generations of progestins
• Available in cyclic formulations (21-24 days of active pills followed by 4-7 days of placebo), extended cyclic formulations, or continuous formulations 1

Biphasic Oral Contraceptives

• Contain two different dosage combinations of estrogen and progestin during the cycle
• Typically have one hormone combination for the first phase of the cycle, followed by a different combination for the second phase
• Designed to more closely mimic hormonal fluctuations of the natural menstrual cycle
• Less commonly prescribed than monophasic or triphasic pills
• Limited evidence suggests no clear advantage over monophasic pills 2

Triphasic Oral Contraceptives

• Contain three different dosage combinations throughout the cycle
• Can vary the progestin dose while keeping estrogen constant, or vary both hormones
• Developed to further mimic the natural hormonal fluctuations during the menstrual cycle
• Originally designed to reduce total hormone exposure while maintaining efficacy
• May have varying levels of estrogen and/or progestin during each week of active pills 3, 4

Comparative Aspects

Efficacy

• All three types have similar contraceptive efficacy when used correctly
• A Cochrane review found insufficient evidence to determine whether triphasic OCs differ from monophasic OCs in effectiveness 5
• No significant differences in pregnancy prevention rates have been demonstrated between the different phasic formulations

Cycle Control and Bleeding Patterns

• Some studies suggest triphasic pills may offer better cycle control than monophasic pills, but evidence is inconsistent
• Triphasic pills containing newer progestins (desogestrel, gestodene, norgestimate) may have better cycle control and reduced androgenic side effects compared to those with older progestins 4
• However, meta-analysis has been difficult due to differences in measuring and reporting cycle disturbance data 5

Side Effects

• Early studies suggested that triphasic pills might reduce side effects compared to the original high-dose monophasic pills 3
• Modern low-dose monophasic and triphasic pills have similar side effect profiles
• No significant differences have been found in discontinuation rates due to side effects between monophasic and triphasic formulations 5

Clinical Implications

• Monophasic pills are generally recommended as first-line options due to their simplicity and extensive evidence base 5
• The choice of progestin (generation and type) may be more important than the phasic regimen in determining bleeding patterns and side effects 6
• Newer progestins (fourth generation) like drospirenone may have additional benefits such as anti-mineralocorticoid activity that can help mitigate blood pressure effects 1
• Newer estrogen formulations (estradiol valerate, estetrol) may offer improved safety profiles compared to ethinyl estradiol 1

Common Pitfalls

• Assuming that triphasic pills are inherently superior to monophasic pills; current evidence does not strongly support this
• Focusing only on the phasic nature of the pill rather than considering the specific hormones and their doses
• Overlooking the importance of the progestin type, which may have more impact on side effects than whether the pill is monophasic or multiphasic
• Failing to consider that simpler regimens (monophasic) may lead to better adherence for some patients

Despite theoretical advantages of multiphasic pills in mimicking natural cycles, the available evidence does not consistently demonstrate superior outcomes compared to monophasic formulations. The choice between monophasic, biphasic, and triphasic oral contraceptives should consider factors such as the specific hormones used, their doses, and individual response patterns.