Inclusion Criteria:

1. Male and female patients, aged 18 and above

2. Suffering from functional constipation, according to their medical history, as defined by the Rome III diagnostic criteria , i.e.:Criteria fulfilled for the last 3 months with symptom onset at least 6 months prior to diagnosis.

   1. Must include 2 or more of the following::

      • straining during at least 25% of the defecations
      • lumpy or hard stools in at least 25% of the defecations
      • sensation of incomplete evacuation for at least 25% of the defecations
      • sensation of anorectal obstruction/blockade for at least 25% of the defecations
      • manual manoeuvres to facilitate at least 25% of the defecations (e.g. digital evacuation, support of the pelvic floor)
      • fewer than 3 defecations per week
   2. Loose stools are rarely present without the use of laxatives
   3. There are insufficient criteria for irritable bowel syndrome (IBS)
3. Able and willing to complete a daily e-diary
4. Able and willing to use the trial rescue medication

5. Signed and dated written informed consent prior to enrolment into the study in accordance with GCP and local legislation

   At Visit 2, patients must comply with the following additional inclusion criteria to be eligible for entry into the treatment phase:

6. Functional constipation is confirmed by e-diary data at the end of the baseline period:

   a. An average of less than 3 CSBMs per week, together with at least one of the following symptoms occurring at least 25% of the time:

   • straining
   • incomplete evacuation
   • lumpy or hard stools (i.e. type 1 or type 2 stools)
7. Compliant with the use of the e-diary throughout the baseline period (compliance is defined as completing 80% of the evening reports)

8. Compliant with the use of rescue medication throughout the baseline period. Compliance is defined as follows:

   • rescue medication may be used if there has not been a bowel movement for more than 72 hrs rescue medication may not be used on either day -1 or on the day of randomisation (day 1)

Exclusion Criteria:

1. Eating disorders such as anorexia nervosa and bulimia, as a cause of excessive use of laxatives
2. Patients whose constipation is caused by primary organic disease of the colon or pelvic floor
3. Patients with metabolic disorders, neurological disorders, severe or psychiatric disorders, or any other significant disease or intercurrent illness (e.g. abdominal/gastrointestinal surgery) that, in the Investigators¿ opinion, would interfere with participation in the trial
4. Patients with restricted mobility (e.g. wheelchair bound, or bed-ridden) that, in the Investigators¿ opinion, would interfere with participation in the trial
5. Patients with a known hypersensitivity to bisacodyl or any other ingredient in the study medication
6. Patients with ileus, intestinal obstruction, acute surgical abdominal conditions (such as acute appendicitis and acute inflammatory bowel diseases), or severe dehydration
7. Patients with anal fissures or ulcerative proctitis with mucosal damage
8. Patients with known clinically significant abnormal electrolyte values
9. Patients whose concomitant therapy includes an opioid medication (e.g. morphine, codeine)
10. Constipation which, in the Investigators¿ opinion, is caused by medication (e.g. anticholinergics)
11. Patients who are not willing to discontinue the use of prohibited concomitant therapy

12. Pre-menopausal women who:

    1. are nursing (breast-feeding) or who are pregnant OR

    2. who are of child-bearing potential and are not practicing an acceptable method of birth control, or do not plan to continue using this method throughout the study. Acceptable methods of birth control include:

       • transdermal patch
       • intra-uterine devices/systems (IUDs/IUSs)
       • oral, implantable or injectable contraceptives
       • sexual abstinence
       • sterilisation or a vasectomised partner
13. Participation in another trial with an investigational product with 1 month of enrolment into this study
14. Drug or alcohol abuse